Various types of medical electrical leads for use in cardiac rhythm management (CRM) and neurostimulation applications are known. In CRM applications, for example, such leads are frequently delivered intravascularly to an implantation location on or within a patient's heart, typically under the aid of fluoroscopy. Once implanted, the lead is coupled to a pulse generator or other implantable device for sensing cardiac electrical activity, delivering therapeutic stimuli, and/or for performing other desired functions within the body. Such leads typically include a distal conductor end with one or more electrodes that contact the heart tissue, and a proximal terminal end that is connected to a pacemaker or defibrillator. The conductor end of the lead can include one or more features such as an active fixation helix or a number of passive tines to facilitate securing the lead to the heart tissue. The terminal end of the lead, in turn, includes one or more electrical contacts that are electrically connected to the electrodes via a number of lead conductors.
An increase in the stimulation threshold required to electrically stimulate the body can result from the interaction of the electrodes with the body tissue at the site of implantation. In CRM applications involving leads implanted in or near the heart, for example, the capture threshold of the lead can increase due to the formation of scar tissue at the location where the electrodes contact the body tissue. Approaches to reducing the capture threshold have included the incorporation of drug-eluting collars or plugs containing a therapeutic drug such as dexamethasone acetate, which reduces inflammation at the site of contact.
The incorporation of drug-eluting collars or plugs into medical electrical leads is typically accomplished via an injection molding process in which the collar or plug is pre-formed as a separate component, and then subsequently bonded to the lead body via an adhesive or glue. In the fabrication of medical electrical leads used in CRM and neurostimulation applications, for example, the drug-eluting collar is typically formed in a mold and then adhesively bonded onto a distal portion of the lead, typically adjacent to an electrode located at the distal end of the lead body. In some cases, variability in the contact surface area at the location of the adhesive can cause the rate at which the drug is eluted into the body tissue to vary. Some drug collar bonding techniques can also result in yield fallout and other manufacturing issues.